In the wireless communication, if both a transmitting end and a receiving end use a plurality of antennas, the spatial multiplexing mode can be adopted to acquire higher rate, thus to improve the transmission rate. At the receiving end the channel matrix passed through by the transmitted signal can be obtained by channel estimation, therefore, although each antenna transmits different data, after passing through the MIMO signal matrix, the transmitted data on each antenna can still be decoded at the receiving end.
Compared with the method for directly decoding the transmitted data on each antenna by using the channel matrix, an enhanced method is to use a transmission pre-coding technology. The concept of layer is defined at the transmitting end, on the same time-frequency resource, different data symbols might be transmitted in each layer, and the number of layers is equal to the rank of the channel matrix. The data in each layer are pre-coded and mapped to the antenna, and then transmitted to the receiving end through the air channel. If the transmitting end is able to know the complete and accurate Channel State Information (CSI), we can carry out the Singular Value Decomposition (SVD) on the specific channel matrix. And then the matrix consisting of the right eigenvectors decomposed from the channel matrix is taken as the pre-coding matrix to pre-code the data in each layer.
However, usually only the receiving end can directly and accurately get the CSI, and the transmitting end acquires the CSI only by feeding back the CSI information to the transmitting end via the receiving end. In the current mainstream standards, the feedback capacity provided by the system for the CSI information is relatively limited, because the feedback amount for feeding back the entire channel information is very huge. Therefore, the mainstream feedback methods are all based on the codebook mode, and the feedback content is the quantitative information of the matrix consisting of the right eigenvectors of the channel, and the quantitative information is represented by the codewords in the codebook.
The basic principle of the pre-coding based on codebook feedback is that, assuming the limited feedback channel capacity is B bps/Hz, the number of available codewords is N=2B. All of the pre-coding matrixes are quantitated to construct the codebook ={F1, F2 . . . FN}. The transmitting end and the receiving end store the codebook together. For the channel matrix H obtained by each channel estimation, the receiving end selects a codeword {circumflex over (F)} (which can be called as the optimal codeword) from  according to the preset criteria, and feeds back the serial number i corresponding to the codeword {circumflex over (F)} to the transmitting end. The transmitting end finds out the pre-coded codeword {circumflex over (F)} according to the serial number i and pre-codes the transmitted symbol block.
In general,  can be further divided into codebooks corresponding to a plurality of Ranks, and each Rank corresponds to a plurality of values to quantitate a pre-coding matrix consisting of the channel right eigenvectors under this Rank. Since the number of the Ranks of channel and the number of the non-zero right eigenvectors are equal, generally when the Rank is N, there are N columns of codewords. Therefore, the codebook  can be divided into a plurality of sub-codebooks according to the Rank, shown as table 1:
TABLE 1 The number of layers υ(Rank)12. . .N 1 2. . . Nthe codewordthe codewordthe codewordvector setvector setvector setwhose columnwhose columnwhose columnnumber is 1number is 2number is 3
Because of the limitation of the feedback overhead, only the feedback based on the codebook can be used to transmit the pre-coding.
Wherein, when the Rank>1, all of the codewords that need to be stored are in the form of matrix, wherein, the codebook in the LTE protocol uses this feedback method of the codebook quantitation, the downlink 4 transmission antennas codebook in the LTE is shown as table 2 in the following, and in fact the pre-coding codebook and the channel information quantitation codebook in the LTE have the same meaning. In the following, for the sake of consistency, a vector can also be considered as a one-dimensional matrix.
TABLE 2The total number of layers υCodebook indexun12340u0 = [1 −1 −1 −1]TW0{1}W0{14}/{square root over (2)}W0{124}/{square root over (3)}W0{1234}/21u1 = [1 −j 1 j]TW1{1}W1{12}/{square root over (2)}W1{123}/{square root over (3)}W1{1234}/22u2 = [1 1 −1 1]TW2{1}W2{12}/{square root over (2)}W2{123}/{square root over (3)}W2{3214}/23u3 = [1 j 1 −j]TW3{1}W3{12}/{square root over (2)}W3{123}/{square root over (3)}W3{3214}/24u4 = [1 (−1 − j)/{square root over (2)} −j (1 − j)/{square root over (2)}]TW4{1}W4{14}/{square root over (2)}W4{124}/{square root over (3)}W4{1234}/25u5 = [1 (1 − j)/{square root over (2)} j (−1 − j)/{square root over (2)}]TW5{1}W5{14}/{square root over (2)}W5{124}/{square root over (3)}W5{1234}/26u6 = [1 (1 + j)/{square root over (2)} −j (−1 + j)/{square root over (2)}]TW6{1}W6{13}/{square root over (2)}W6{134}/{square root over (3)}W6{1324}/27u7 = [1 (−1 + j)/{square root over (2)} j (1 + j)/{square root over (2)}]TW7{1}W7{13}/{square root over (2)}W7{134}/{square root over (3)}W7{1324}/28u8 = [1 −1 1 1]TW8{1}W8{12}/{square root over (2)}W8{124}/{square root over (3)}W8{1234}/29u9 = [1 −j −1 −j]TW9{1}W9{14}/{square root over (2)}W9{134}/{square root over (3)}W9{1234}/210u10 = [1 1 1 −1]TW10{1}W10{13}/{square root over (2)}W10{123}/{square root over (3)}W10{1324}/211u11 = [1 j −1 j]TW11{1}W11{13}/{square root over (2)}W11{134}/{square root over (3)}W11{1324}/212u12 = [1 −1 −1 1]TW12{1}W12{12}/{square root over (2)}W12{123}/{square root over (3)}W12{1234}/213u13 = [1 −1 1 −1]TW13{1}W13{13}/{square root over (2)}W13{123}/{square root over (3)}W13{1324}/214u14 = [1 1 −1 −1]TW14{1}W14{13}/{square root over (2)}W14{123}/{square root over (3)}W14{3214}/215u15 = [1 1 1 1]TW15{1}W15{12}/{square root over (2)}W15{123}/{square root over (3)}W15{1234}/2Wherein,Wn = I − 2ununH/unHun, I is a unit matrix, and Wk(j) denotes the jth column vector of the matrix Wk.Wk(j1,j2, . . . jn) denotes the matrix consisting of the j1, j2, . . . jn columns of the matrix Wk.
With the development of the communication technology, there is a higher demand for the spectrum efficiency in LTE-Advanced, therefore the number of antennas is increased to 8, and we need to design the codebook feedback of 8 transmission antennas to carry out the quantitation feedback of the channel information.
In the LTE standard, the smallest feedback unit of the channel information is subband, one subband consists of several Resource Blocks (RBs), each RB consists of a plurality of Resource Elements (REs), the RE is the smallest unit of time-frequency resource in the LTE, and in the LTE-A, the resource representation method in the LTE continues to use.
In the practical system, the low-rank codebook is most often used, therefore the codebook design of Rank=1 and Rank=2 is very important in the codebook design. In the 4 antennas (Tx) codebook, there is a relatively mature codebook construction method, while in the 8 antennas, due to the increase of the antenna dimension, the mainstream application scenario at the transmitting end changes from the single-polarized antenna to the dual-polarized antenna, therefore, a new 8 antennas codebook needs to be designed.
In the 8 antennas codebook of Rank=1 and Rank=2, two parts of codewords are usually included, one part considers for matching the relevant channel characteristics and the other part considers for matching the irrelevant channel characteristics, and the codeword considering for matching the relevant channel characteristic is the most important consideration. Considering the channel model and the polarization of the antenna, etc., the codeword can have minimum quantitation error for the channel information. Meanwhile, the other codewords only need to be distributed as evenly as possible, even the other codewords can be separated from the codewords that match the relevant channel. We can make the distribution of the codewords even by using a minimal chord distance maximal rule between the codewords.
For example, the first 8 DFT codewords of 16 codewords of the Rank1 in the LTE are designed for the relevant channel, and are very suitable for the relevant channel of the single-polarized antenna, while the last 8 codewords are added based on the first 8 codewords, which guarantees that the 16 codewords can be better distributed in the 4-dimensional multiplex space after increasing to the 16 codewords.
Of course, since the codeword for matching the relevant channel can also be used to match the irrelevant channel, regardless of the optimal performance under the irrelevant channel, the codebook only comprises the codewords for matching the relevant channel. For example, in the process of the LTE discussion, there is a technical scheme in which all of the 16 Rank1 codewords use the DFT codewords suitable for the relevant channel of the single-polarized antenna as the codebook.
Generally in the codebook of Rank=1 or Rank=2 there are K codewords for matching (suitable for) the relevant channel. The other codewords match the irrelevant channel, and this part of codewords might be 0.
So far in the existing codebook technology, when the number of the codewords in Rank=1 or Rank=2 is 16, the number of the codewords for matching the relevant channel is 8 at Rank=1 and Rank=2.
Specify the following values in Table 3:
TABLE 3u #v #u0[1 1 −1 −1 1 1 −1 −1]TV0[1 1 1 1]Tu1[1 q3 −j q2 1 q1 j q0]TV1[1 −j −1 −j]Tu2[1 −j −1 j −1 −j −1 j]TV2[1 −1 1 −1]Tu3[1 q2 j q3 1 q0 −j q1]TV3[1 −j −1 j]Tu4[1 −1 1 1 1 −1 1 −1]TV4[1 q0 j q1]Tu5[1 q1 −j q0 1 q3 j q2]TV5[1 q1 −j q0]Tu6[1 j −1 −j 1 j 1 −j]TV6[1 q2 j q3]Tu7[1 q0 j q1 1 q2 −j q3]TV7[1 q3 −j q2]TWherein,q0 = (1 + j)/{square root over (2)};q1 = (−1 + j)/{square root over (2)};q2 = (−1 − j)/{square root over (2)};q3 = (1 − j)/{square root over (2)}.
In the codebook of Rank=1 and Rank=2, the codewords for matching the relevant channel are shown as Table 4:
TABLE 4IndexRank1 codebookRank2 codebook 1Rank2 codebook 20u0[u0,u1]kron(I,v0)*U1u1[u1,u2]kron(I,v1)*U2u2[u2,u3]kron(I,v2)*U3u3[u3,u4]kron(I,v3)*U4u4[u4,u5]kron(I,v4)*U5u5[u5,u6]kron(I,v5)*U6u6[u6,u7]kron(I,v6)*U7u7[u7,u0]kron(I,v7)*U8-15the codewords for matching the irrelevant channel  Wherein  ,            I      =              [                                            1                                      0                                                          0                                      1                                      ]              ;          U      =                        [                                                    1                                            1                                                                    1                                                              -                  1                                                              ]                ⁢                  /                ⁢                  2                      ;  
However, after pre-coding the codebook of Rank=1 in the related art, with the single-polarized and dual-polarized antenna, the evenly distributed wave beam in the cell direction (120 degrees or 180 degrees) is not formed at the relevant channel, and channel direction information of each UE in the cell is not well quantitated. Furthermore, the formed wave beam has relatively large side lobe, and the power of the main lobe is not concentrated, which results in the performance loss. Wherein, the wave beam pattern obtained in the case of the single-polarized antenna is shown as FIG. 1 (the number of codewords for matching the relevant channel is 8). While in the case of the dual-polarized antenna and the relevant channel, by a simulation experiment, the average quantitation matching degree is less than 0.5.
When Rank=2, taking the implementation complexity and storage problem at the UE end into account, the system can only select one codebook to use, but the codebook 1 has a relatively better performance in the case of the single-polarized antenna, while has a poor performance in the case of the dual-polarized antenna; whereas, the codebook 2 of Rank=2 has a good performance in the case of the dual-polarized antenna, and has a poor performance in the case of the single-polarized antenna.